Characterization of intertidal flat hydrodynamics

Abstract

The paper reviews the di!erent physical forcings that control tidal #at hydrodynamics. Tidal propagation and cross-shore or long-shore currents, tidal asymmetry, wind-induced circulation, wave propagation and drainage processes are successively considered. Some simple methods are described for estimating cross-shore currents and wave-induced bottom shear stresses, and the results obtained are compared to "eld measurements on three contrasted sites in Europe. In particular the cross-shore current is shown uniform in the lower part of the #at, and decreasing towards the shore. Bottom friction-induced wave attenuation is simply formulated on gently sloping beds, leading to a maximum wave height that a #at can experience; it is proportional to the water height according to the ratio between the slope and the wave friction factor. The maximum related shear stress occurs at high water and is also proportional to the water depth. Maximum tidal velocities are very similar in the three sites where bottom sediment is muddy, suggesting a relationship between physical stresses and sediment characteristics. The consequences of physical forcings on sediment transport are listed. The bottom shear stress is suggested as the relevant parameter for comparing tidal and wave e!ects. In general, tide induces onshore sediment transport, whereas waves and drainage favour o!shore transport. The processes leading to a possible tidal equilibrium pro"le are analysed: they involve the intrinsic asymmetry that favours net deposition at high water, and an ebb dominance generated by the resulting bottom pro"le convexity. Eroding waves are likely to upset such a balance; this equilibrium then reduces to a trend for the system.

Net sediment transport in tidal basins: quantifying the tidal barotropic mechanisms in a unified framework

“…Tidal asymmetries are especially due to shallow-water overtides (Dronkers 1986;Friedrichs and Aubrey 1988;Ridderinkhof 1988;Le Hir et al 2000). The impact on sediment transport is stronger for shallow seas like the North Sea (semidiurnal regime), since a significant M4 component is already present at the inlet.…”

Modeling sorting dynamics of cohesive and non-cohesive sediments on intertidal flats under the effect of tides and wind waves

“…Wind waves, either depth-or fetch-limited (Fagherazzi and Wiberg, 2009;Mariotti and Fagherazzi, 2013), can lead to large sediment re-suspension on shallow tidal flats (see Green and Coco, 2013 for a review). Existing field measurements and numerical studies suggest that waves generally favor the offshore sediment transport and result in the erosion of tidal flats (Bassoullet et al, 2000;Roberts et al, 2000). Sediment supply (fluvial or marine) can pronouncedly alter the width and the overall shape of tidal flats, even at a seasonal scale (Liu et al, 2011).…”

A model of sediment transport over an intertidal transect, comparing the influences of biological and physical factors

“…Intertidal areas have frequently been modeled as part of two-dimensional or three-dimensional models of whole estuaries (Cheng et al 1993;le Hir et al 2000). These models are larger and more complex than is needed for our purpose here, which is more an experimental investigation into combining processes rather than a predictive model for a particular area.…”